The present invention relates generally to a zoom lens and imaging apparatus, and more particularly to a zoom lens that is made much more compact and so lends itself to imaging apparatus inclusive of video cameras and digital cameras.
In recent years, attention has been paid to digital cameras as the next-generation cameras superceding film cameras. Those cameras have some wide categories from commercial high-end types to portable low-end types.
For digital cameras or video cameras falling under the portable low-end type category, there are mounting demands toward depth direction size reductions while making sure high image quality. The depth direction of a camera is significantly affected by the thickness of a lens system from an object-side surface to an imaging plane. Zoom lenses in particular tend to increase in terms of that thickness as images are being taken. For this reason, use of the so-called collapsible lens mount is now in vogue, in which the zoom lens is let out of a camera body as images are being taken while it is put away in the camera body as it is carried around.
Among compact zoom lenses so far known in the art, there is a so-called negative-power-ahead type zoom lens comprising, in order from its object side, a first lens group having negative refracting power, a second lens group having positive refracting power and a third lens group having positive refracting power, with its examples set forth in:
Patent Publication 1: JP(A)2002-142484
Patent Publication 2: JP(A)2003-177315
Patent Publication 3: JP(A)2007-65590
However, the zoom lens of Patent Publication 1 works against size reductions of a camera, because the first lens group having negative refracting power includes two lenses with an air spacing between them: the thickness of the first lens group on an optical axis is likely to increase, so that the thickness direction size of a lens barrel is not sufficiently thin even upon received at a lens mount.
The zoom lens of Patent Publication 2 may work for size reductions, because the first lens group having negative refracting power is made up of one negative lens. However, the use of one negative lens alone is likely to give rise to some considerable fluctuations of astigmatism and chromatic aberrations at the wide-angle end or during zooming, rendering it difficult to obtain high zoom ratios.
The zoom lens of Patent Publication 3 may work for size reductions and reductions of chromatic aberrations at the first lens group, because the first lens group having negative refracting power is made up of one lens component having a negative lens and a positive lens (the lens component here is defined as a lens block wherein surfaces contacting air on the optical axis are only two, i.e., an entrance surface and an exit surface). However, it works against making sure the angle of view and brightness because it is difficult to hold back fluctuations of astigmatism and so on.
In view of such problems as mentioned above, one object of the present invention is to provide a zoom lens that goes in favor of size reductions upon received at a lens mount, and enables optical performance to be easily kept intact even when the zoom ratio, brightness, and angle of view is ensured as desired.
Another object is to provide an imaging apparatus equipped with such a zoom lens.